ABSTRACT This project seeks to increase our understanding of the nature of physical activity carried out by persons with chronic heart failure (CHF) and characterize the level and types of physical activity identified as being important and meaningful in their daily lives, which will address an unmet need in CHF drug development. The evidence generated by this project is necessary to support the qualification of an activity monitor-based endpoint measure by the Food and Drug Administration's (FDA's) Clinical Outcome Assessment (COA) Qualification Program. This qualification effort is being led by the Patient-Reported Outcome (PRO) Consortium's CHF Working Group, for which an activity monitor-based endpoint measure was one of three measures accepted into the COA Qualification Program. In order to progress to the next stage of qualification, the CHF Working Group must prepare a Qualification Plan which defines the concept of interest being assessed by the COA in the specific context of use. To date, the CHF Working Group has not defined these activity monitor-related concepts of interest, nor have they been found in the published literature. To address this gap, the Critical Path Institute (C-Path) proposes the following research aim 1: to conduct a stratified, non-interventional, qualitative concept elicitation study in 40 patients (both male and female) with CHF, from across the United States (US). The study will use a stratified design to ensure balance and contribution from CHF patients with either preserved ejection fraction (HFpEF) or reduced ejection fraction (HFrEF), including NYHA grades II through IV. Diagnosis will be confirmed by medical record review by the referring clinician. Consenting patients will participate in a 60- to 90-minute interview with a trained qualitative interviewer following a semi-structured interview guide. The interviews will be transcribed, and transcripts will be coded and analyzed thematically. A report will be produced summarizing the study results for inclusion in future qualification milestone submissions. In addition, research aim 2 is to reach consensus with FDA on the activity monitor-based concept of interest following submission of the study report, which will support the future submission of a Qualification Plan for DDT# 000114 in order to further the development of the activity monitor-based endpoint measure to assess physical activity in CHF clinical trials. In addition to providing insights for CHF research, this research may serve as a proof of concept to demonstrate a methodology to apply patient-focused drug development principles to the development of concepts of interest using wearable devices, such as accelerometers.